This invention relates generally to medical devices, and more particularly concerns an improved ultrasound transmission member for use in an ultrasonic catheter for treatment of blockages of hollow anatomical structures.
In typical percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter having a preformed distal tip is percutaneously introduced into the cardiovascular system of a patient through the brachial or femoral arteries and is advanced therein until the distal tip thereof is in the ostium of the desired coronary artery. A guide wire and a dilatation catheter having a balloon on the distal end thereof are introduced through the guiding catheter with the guide wire slidably disposed within an inner lumen of the dilatation catheter. The guide wire is first advanced into the patient""s coronary vasculature until the distal end thereof crosses the lesion to be dilated and then the dilatation catheter is advanced over the previously introduced guide wire until the dilatation balloon is properly positioned across the lesion. The balloon may then be inflated to treat the lesion. Thereafter, a stent device may be located at the treated lesion, if deemed necessary.
In xe2x80x9cultrasonicxe2x80x9d angioplasty, an ultrasonic angioplasty catheter is similarly advanced to an area of vascular blockage, and mechanical vibration at ultrasonic frequencies, generated typically by a piezoceramic transducer, is delivered along an ultrasonic angioplasty transmission member or wire to a distal catheter tip. When the distal catheter tip is abutted against intravascular blockage, the vibration of the distal end of the ultrasonic angioplasty transmission member removes the obstruction by mechanical impact and cavitation.
Ultrasonic angioplasty transmission members are commonly connected to an extra-corporeal source of ultrasonic energy, so that it is generally necessary to deliver the ultrasonic energy over a relatively long distance, such as approximately 150 cm., to the intravascular blockage to be treated. Over such a distance, the ultrasonic energy attenuates as it passes along the length of the ultrasonic angioplasty transmission member, resulting in a loss of system efficiency, and requiring the delivery of a greater amount of acoustic energy to the ultrasonic angioplasty transmission member than actually reaches the treatment site, which can increase fatigue of the ultrasonic angioplasty transmission member and thereby increase the chances of fracturing and breakage during use, especially when the wires are bent. It is therefore desirable to provide an ultrasonic angioplasty transmission member that has a lower loss of the ultrasonic energy transmitted by the member so that lower levels of energy may be applied to the member.
In ultrasonic angioplasty techniques, accurate positioning of the ultrasound transmission member in the vasculature system to be treated requires a highly flexible ultrasonic delivery system with a low profile, especially for coronary ultrasonic angioplasty procedures, so that the catheter can more easily navigate the various vascular passages to be advanced to the occlusion. Nickel-titanium superelastic alloys have been useful in these respects as an ultrasound transmission member. Tapering or narrowing the distal end of an ultrasound transmission member to enhance flexibility of the ultrasound transmission member at its distal end is known from U.S. Pat. No. 5,304,115 (Pflueger et al.), issued Apr. 19, 1994. While such tapering or narrowing typically decreases the rigidity and improves the bendability of the ultrasound transmission member, a significant increase in amplitude of the ultrasonic energy occurs at the tapered or narrowed region. Such an increase in amplitude can cause an increased likelihood of fracturing or breakage of the ultrasound transmission member at that point during use.
Ultrasonic angioplasty transmission members that are surface hardened to reduce fracturing or breakage are disclosed in U.S. Pat. No. 5,304,115 to Pflueger et al. The ultrasound transmission members of U.S. Pat. No. 5,304,115 can be formed of one or more superelastic metal alloys, commonly known as the xe2x80x9cshape memory alloys,xe2x80x9d such as a nickel-titanium alloy containing 50.8 atomic percent nickel, with a surface treatment of titanium nitride on the ultrasound transmission member to lower the coefficient of friction and/or increase the surface hardness of all or a portion of the ultrasound transmission member to reduce the chances of fracturing during high cycle fatigue that can occur in uncoated titanium or aluminum ultrasound transmission members.
While it is desirable to protect the outer surface of ultrasonic angioplasty transmission wires from fracturing by hardening of the outer surface, it is also desirable that such ultrasonic angioplasty transmission wires efficiently transmit sound at ultrasonic frequencies, have good tensile strength, and have a selected degree of flexibility suitable for navigating the various types of sharp bends and curves encountered in the vasculature of a patient. In general, a percutaneous transluminal angioplasty catheter may be selected to be shorter and stiffer, while a percutaneous transluminal coronary angioplasty catheter may be selected to be longer and more flexible.
Selection of a single material of the ultrasonic angioplasty transmission wire for a desired range of flexibility can at the same time affect the tensile strength, sonic properties and fatigue strength of the wire making the wire for different applications. For example, forming an ultrasonic angioplasty transmission wire of one selected ultrasound transmitting material for a desired range of flexibility of the ultrasonic angioplasty transmission wire can adversely affect the desired range of wave lengths that can be suitably transmitted in the wire, affecting the sonic transmission properties and transmission efficiency over the overall length of the catheter. In turn, forming the ultrasonic angioplasty transmission wire of one ultrasound transmitting material to improve the properties of the ultrasonic angioplasty transmission wire for transmitting a desired range of wave lengths can adversely affect the desired flexibility of the ultrasonic angioplasty transmission wire.
Hence, those skilled in the art have recognized the need for providing a structure for an ultrasonic angioplasty transmission member that allows for the use of different ultrasound transmitting materials and thicknesses to allow alteration and selection of properties of the ultrasonic angioplasty transmission member such as sonic transmission, flexibility and tensile strength, that are improved over those properties of a comparable wire formed of a single material. There is also a need for construction of an ultrasonic angioplasty transmission member that reduces attenuation of ultrasonic energy transmitted along the length of the ultrasonic angioplasty transmission member, to reduce the loss of system efficiency, and to in turn reduce the requirement for the delivery of a higher amounts of acoustical energy to the ultrasonic angioplasty transmission member, to reduce the fatigue, fracturing and breakage of the ultrasonic angioplasty transmission member that can be a consequence of high acoustical energies during use. The present invention fulfills these needs and others.
Briefly, and in general terms, the present invention is directed to an improved construction for an ultrasonic angioplasty transmission member that allows alteration of the properties of sonic transmission, flexibility, and tensile strength by providing the member with selected layering of different ultrasound transmitting materials and thicknesses of materials. In one aspect, the invention is directed to an ultrasound transmission wire for use in an ultrasonic angioplasty device, comprising an inner member of a first ultrasound transmitting material, and a first coaxial shell bonded to the inner member and formed of a second ultrasound transmitting material different from the first ultrasound transmitting material.
In more detailed aspects, the first and second ultrasound transmitting materials are selected from the group consisting essentially of stainless steel, nickel-titanium, aluminum, titanium, and multiphase alloys. Further, the first ultrasound transmitting material consists essentially of a nickel-titanium alloy and the second ultrasound transmitting material consists essentially of stainless steel. In a further aspect, the inner member comprises the core of the wire.
In yet another detailed aspect, the ultrasound transmission wire further comprises a second coaxial shell disposed over the first coaxial shell, the second coaxial shell comprising the first ultrasound transmitting material. The first and second ultrasound transmitting materials are selected from the group consisting essentially of stainless steel, nickel-titanium, aluminum, titanium, and multiphase alloys. The first ultrasound transmitting material consists essentially of a nickel-titanium alloy, and the second ultrasound transmitting material consists essentially of stainless steel.
In another detailed aspect, the invention is directed to an ultrasound transmission wire for use in an ultrasonic angioplasty device, comprising an inner member of a first ultrasound transmitting metal composition, a first coaxial tube bonded to the inner member and formed of a second ultrasound transmitting metal composition different from the first ultrasound transmitting metal composition, and a second coaxial tube bonded to the outer coaxial tube and formed of the first ultrasound transmitting metal composition.
In another main aspect, the present invention is directed to an ultrasonic angioplasty catheter device comprising an elongate flexible catheter having a proximal end, a distal end, and at least one lumen extending longitudinally therethrough, the device comprising an ultrasound transmission member extending through said lumen and having a distal end with a distal head fixed in position in the catheter for applying ultrasonic energy to an occlusive lesion, and a proximal end configured to be connected to an ultrasound generating device, wherein the distal head comprises a larger diameter distal portion positioned beyond the distal end of the catheter and a smaller diameter portion located between the distal portion and the ultrasound transmission member and extending within the catheter and wherein the ultrasound transmission member comprises a core of a first ultrasound transmitting material and a first coaxial shell bonded to the inner member and formed of a second ultrasound transmitting material different from the first ultrasound transmitting material, and a second coaxial shell disposed over the first coaxial shell, the second coaxial shell comprising the first ultrasound transmitting material.